1. Field of the Invention
The present invention relates to a method of grinding the rear side of a semiconductor wafer, on the front side of which bumps are formed.
2. Related Art
Referring to FIG. 11, a semiconductor wafer W1 has ICs, LSIs or other circuits formed on its front side, and a protection tape T1 is applied to the front side of the semiconductor wafer W1. The semiconductor wafer W1 is put on a chuck table 50 with its front side down, and the semiconductor wafer W1 is ground to a predetermined thickness by applying the grindstone 51 to its rear side and by rotating the grindstone 51.
Referring to FIG. 12, a semiconductor wafer W2 has terminals 52 (called xe2x80x9cbumpsxe2x80x9d) formed on its front side. A protection tape T2 whose adhesive layer is thick enough to bury the bumps 52, is applied to the front side. Alternatively a protection tape coated with ultraviolet-sensitive glue may be attached to the front side of the semiconductor wafer W2, and the tape is exposed to ultraviolet rays prior to the grinding so that the glue may be set. Thus, the stress applied to each bump is reduced in grinding so that the semiconductor wafer W2 may be prevented from cracking.
In either case the stress applied to the bumps 52 cannot be removed completely, and therefore, the cracking of semiconductor wafers cannot be prevented completely. Also, the necessity of using extra tapes as described above is economically disadvantageous.
It is, therefore, required that the cracking of semiconductor wafers having bumps formed on their front sides be completely prevented in grinding their rear sides without involving extra costs.
To meet such requirement a method of grinding the rear side of a semiconductor wafer according to the present invention comprises the steps of: preparing semiconductor wafers whose front surfaces have a plurality of circuits formed in lattice patterns; coating the front surface of a selected one of the semiconductor wafers with a resist material to form a resist layer thereon; forming a plurality of holes in the resist layer to extend through the resist layer to the front surface of the semiconductor wafer; forming a plurality of metal bumps to project as bumps from the front surface of the semiconductor wafer such that each of the metal bumps is disposed in one of the holes formed in the resist layer; positioning the semiconductor wafer, which has the metal bumps disposed in the holes of the resist layer, on a chuck table such that the resist layer is supported on the chuck table and the front surface of the semiconductor wafer faces the chuck table; and grinding a rear surface of the semiconductor wafer while the semiconductor wafer is positioned on the chuck table.
The method may further comprise the step of applying a protection tape to the resist layer at the front side of the semiconductor wafer such that, when the semiconductor wafer is positioned on the chuck table, the protection tape is in contact with the chuck table and supports the resist layer and the semiconductor wafer.
The bumps are lower than the thickness of the resist layer, and the bumps may be formed by plating at the holes with gold or a soldering metal, each bump being 50 to 200 xcexcm in diameter, and 50 to 200 xcexcm in height.